Discovery and properties of novel analogues of the aphid pheromones nepetalactone and nepetalactol

BACKGROUND

Pheromones have unique advantages for pest control. Current aphid pheromone research focuses on alarm and sex pheromones. However, practical applications are limited so far, as (E)-β-farnesene has only been investigated to a small extent as an alarm pheromone and only male aphids are targeted by sex pheromones. Previous literature reports electrophysiological responses and repellent behavior of asexual aphids to nepetalactone (1B), therefore our objective was to modify nepetalactone's structure to identify key fragments responsible for repellent effects, as guidance for subsequent modifications and further investigation.

RESULTS

In this study, seven derivatives were designed and synthesized based on nepetalactol (1A) and nepetalactone (1B) as lead compounds. Free-choice tests, conducted using cowpea aphids (Aphis craccivora), revealed that the lactone moiety was crucial for the repellent activity, and the removal of the carbonyl group eliminated the repelling effect. Compound (±)1I, an analogue of nepetalactone (1B), demonstrated a significantly higher repellent value than nepetalactone (1B) at three different concentrations, and even at 0.1 mg/mL it maintained a considerable repellent effect (26.5%). Electrostatic potential and density functional theory calculations supported the importance of the carbonyl group for the repellent effects.

CONCLUSION

The newly discovered para-pheromone (±)1I shows improved repellent effects and potential for development as a novel biological control agent. Based on our innovative findings, analogues with improved efficacy and properties can be designed and prepared. Our research contributes to understanding the effects of structural modifications on pheromone activity and properties, which is crucial for exploring novel pheromone-based products for crop protection. © 2024 Society of Chemical Industry.

Isolation and Structure Determination of New Pyrones from Dictyostelium spp. Cellular Slime Molds Coincubated with Pseudomonas spp

Cellular slime molds are excellent model organisms in the field of cell and developmental biology because of their simple developmental patterns. During our studies on the identification of bioactive molecules from secondary metabolites of cellular slime molds toward the development of novel pharmaceuticals, we revealed the structural diversity of secondary metabolites. Cellular slime molds grow by feeding on bacteria, such as Klebsiella aerogenes and Escherichia coli, without using medium components. Although changing the feeding bacteria is expected to affect dramatically the secondary metabolite production, the effect of the feeding bacteria on the production of secondary metabolites is not known. Herein, we report the isolation and structure elucidation of clavapyrone (1) from Dictyostelium clavatum, intermedipyrone (2) from D. magnum, and magnumiol (3) from D. intermedium. These compounds are not obtained from usual cultural conditions with Klebsiella aerogenes but obtained from coincubated conditions with Pseudomonas spp. The results demonstrate the diversity of the secondary metabolites of cellular slime molds and suggest that widening the range of feeding bacteria for cellular slime molds would increase their application potential in drug discovery.

A derivative of trihydroxynaphthalenone and a pyrone metabolite from the endophytic fungus Talaromyces purpurpgenus

A newly discovered trihydroxynaphthalenone derivative, epoxynaphthalenone (1) involving the condensation of ortho-hydroxyl groups into an epoxy structure, and a novel pyrone metabolite characterized as pyroneaceacid (2), were extracted from Talaromyces purpurpgenus, an endophytic fungus residing in Rhododendron molle. The structures of these compounds were elucidated through a comprehensive analysis of their NMR and HRESIMS data. The determination of absolute configurations was accomplished using electronic circular dichroism (ECD) calculations and CD spectra. Notably, these recently identified metabolites exhibited a moderate inhibitory activity against xanthine oxidase (XOD).

Arzanol, a natural phloroglucinol α-pyrone, protects HaCaT keratinocytes against H2O2-induced oxidative stress, counteracting cytotoxicity, reactive oxygen species generation, apoptosis, and mitochondrial depolarization

Skin oxidative stress results in structural damage, leading to premature senescence, and pathological conditions such as inflammation and cancer. The plant-derived prenylated pyrone-phloroglucinol heterodimer arzanol, isolated from Helichrysum italicum ssp. microphyllum (Willd.) Nyman aerial parts, exhibits anti-inflammatory, anticancer, antimicrobial, and antioxidant activities. This study explored the arzanol protection against hydrogen peroxide (H2O2) induced oxidative damage in HaCaT human keratinocytes in terms of its ability to counteract cytotoxicity, reactive oxygen species (ROS) generation, apoptosis, and mitochondrial membrane depolarization. Arzanol safety on HaCaT cells was preliminarily examined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and microscopic observation. The arzanol pre-incubation (5-100 μM, for 24 h) did not induce cytotoxicity and morphological alterations. The phloroglucinol, at 50 μM, significantly protected keratinocytes against cytotoxicity induced by 2 h-incubation with 2.5 and 5 mM H2O2, decreased cell ROS production induced by 1 h-exposure to all tested H2O2 concentrations (0.5-5 mM), as determined by the 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) assay, and lipid peroxidation (thiobarbituric acid reactive substances [TBARS] method). The 2-h incubation of keratinocytes with H2O2 determined a significant increase of apoptotic cells versus control cells, evaluated by NucView® 488 assay, from the dose of 2.5 mM. Moreover, an evident mitochondrial membrane potential depolarization, monitored by fluorescent mitochondrial dye MitoView™ 633, was assessed at 5 mM H2O2. Arzanol pre-treatment (50 μM) exerted a strong significant protective effect against apoptosis, preserving the mitochondrial membrane potential of HaCaT cells at the highest H2O2 concentrations. Our results validate arzanol as an antioxidant agent for the prevention/treatment of skin oxidative-related disorders, qualifying its potential use for cosmeceutical and pharmaceutical applications.

Production of kojic acid by Aspergillus flavus OL314748 using box-Behnken statistical design and its antibacterial and anticancer applications using molecular docking technique

Kojic acid is a wonderful fungal secondary metabolite that has several applications in the food, medical, and agriculture sectors. Many human diseases become resistant to normal antibiotics and normal treatments. We need to search for alternative treatment sources and understand their mode of action. Aspergillus flavus ASU45 (OL314748) was isolated from the caraway rhizosphere as a non-aflatoxin producer and identified genetically using 18S rRNA gene sequencing. After applying the Box-Behnken statistical design to maximize KA production, the production raised from 39.96 to 81.59 g/l utilizing (g/l) glucose 150, yeast extract 5, KH2PO4 1, MgSO4.7H2O 2, and medium pH 3 with a coefficient (R2) of 98.45%. Extracted KA was characterized using FTIR, XRD, and a scanning electron microscope. Crystalized KA was an effective antibacterial agent against six human pathogenic bacteria (Bacillus cereus, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia, Serratia marcescens, and Serratia plymuthica). KA achieves high inhibition activity against Bacillus cereus, K. pneumonia, and S. plymuthica at 100 μg/ml concentration by 2.75, 2.85, and 2.85 compared with chloramphenicol which gives inhibition zones 1, 1.1, and 1.6, respectively. Crystalized KA had anticancer activity versus three types of cancer cell lines (Mcf-7, HepG2, and Huh7) and demonstrated high cytotoxic capabilities on HepG-2 cells that propose strong antitumor potent of KA versus hepatocellular carcinoma. The antibacterial and anticancer modes of action were illustrated using the molecular docking technique. Crystalized kojic acid from a biological source represented a promising microbial metabolite that could be utilized as an alternative antibacterial and anticancer agent effectively.

In Silico Analysis of the Ga3+/Fe3+ Competition for Binding the Iron-Scavenging Siderophores of P. aeruginosa-Implementation of Three Gallium-Based Complexes in the "Trojan Horse" Antibacterial Strategy

The emergence of multidrug-resistant (MDR) microorganisms combined with the ever-draining antibiotic pipeline poses a disturbing and immensely growing public health challenge that requires a multidisciplinary approach and the application of novel therapies aimed at unconventional targets and/or applying innovative drug formulations. Hence, bacterial iron acquisition systems and bacterial Fe2+/3+-containing enzymes have been identified as a plausible target of great potential. The intriguing "Trojan horse" approach deprives microorganisms from the essential iron. Recently, gallium's potential in medicine as an iron mimicry species has attracted vast attention. Different Ga3+ formulations exhibit diverse effects upon entering the cell and thus supposedly have multiple targets. The aim of the current study is to specifically distinguish characteristics of great significance in regard to the initial gallium-based complex, allowing the alien cation to effectively compete with the native ferric ion for binding the siderophores pyochelin and pyoverdine secreted by the bacterium P. aeruginosa. Therefore, three gallium-based formulations were taken into consideration: the first-generation gallium nitrate, Ga(NO3)3, metabolized to Ga3+-hydrated forms, the second-generation gallium maltolate (tris(3-hydroxy-2-methyl-4-pyronato)gallium), and the experimentally proven Ga carrier in the bloodstream-the protein transferrin. We employed a reliable in silico approach based on DFT computations in order to understand the underlying biochemical processes that govern the Ga3+/Fe3+ rivalry for binding the two bacterial siderophores.

Bioactive α-Pyrone Analogs from the Endophytic Fungus Diaporthe sp. CB10100: α-Glucosidase Inhibitory Activity, Molecular Docking, and Molecular Dynamics Studies

Two α-pyrone analogs were isolated from the endophytic fungus Diaporthe sp. CB10100, which is derived from the medicinal plant Sinomenium acutum. These analogs included a new compound, diaporpyrone F (3), and a known compound, diaporpyrone D (4). The structure of 3 was identified by a comprehensive examination of HRESIMS, 1D and 2D NMR spectroscopic data. Bioinformatics analysis revealed that biosynthetic gene clusters for α-pyrone analogs are common in fungi of Diaporthe species. The in vitro α-glucosidase inhibitory activity and antibacterial assay of 4 revealed that it has a 46.40% inhibitory effect on α-glucosidase at 800 μM, while no antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), Mycolicibacterium (Mycobacterium) smegmatis or Klebsiella pneumoniae at 64 μg/mL. Molecular docking and molecular dynamics simulations of 4 with α-glucosidase further suggested that the compounds are potential α-glucosidase inhibitors. Therefore, α-pyrone analogs can be used as lead compounds for α-glucosidase inhibitors in more in-depth studies.

Antibacterial p-terphenyl and α‑pyrone derivates isolated from the marine-derived actinomycete Nocardiopsis sp. HDN154086

Assisted by OSMAC strategy, one new p-terphenyl and two new α‑pyrone derivates, namely nocarterphenyl I (1) and nocardiopyrone D-E (2-3), were obtained and characterized from the marine sediment-derived actinomycete Nocardiopsis sp. HDN154086. The structures of these compounds were determined on the basis of MS, NMR spectroscopic data and single-crystal X-ray diffraction. Compound 1 with a rare 2,2'-bithiazole structure among natural products showed promising activity against five bacteria with MIC values ranging from 0.8 to 1.6 μM and 3 exhibited notable antibacterial activity against MRSA compared the positive control ciprofloxacin.

Sesquiterpenes and α-pyrones from an endophytic fungus Xylaria curta YSJ-5

Chemical investigation of the culture extract of an endophyte Xylaria curta YSJ-5 from Alpinia zerumbet (Pers.) Burtt. et Smith resulted in the isolation of eight previously undescribed compounds including five eremophilane sesquiterpenes xylarcurenes A-E, one norsesquiterpene xylarcurene F, and two α-pyrone derivatives xylarpyrones A-B together with eight known related derivatives. Their chemical structures were extensively established based on the 1D- and 2D-NMR spectroscopic analysis, modified Mosher's method, electronic circular dichroism calculations, single-crystal X-ray diffraction experiments, and the comparison with previous literature data. All these compounds were tested for in vitro cytotoxic, anti-inflammatory, α-glucosidase inhibitory, and antibacterial activities. As a result, 6-pentyl-4-methoxy-pyran-2-one was disclosed to display significant antibacterial activity against Staphylococcus aureus and methicillin-resistant S. aureus with minimal inhibitory concentration value of 6.3 μg/mL.

Undescribed α-pyrone-containing mycotoxins and an eremophilane-type sesquiterpenoid isolated from Aspergillus aureoterreus and their cytotoxicity

Four previously undescribed and highly oxygenated α-pyrone-containing mycotoxins designated citreoviridins (E‒H), and an unreported eremophilane-type sesquiterpenoid namely aureoterrolide N, were isolated from the culture broth of Aspergillus aureoterreus. Those isolates were inferred from extensive spectroscopic methods and theoretical computation, where their absolute configurations were unambiguously determined by coupling constants following an empirical rule for the acyclic vicinal diol, theoretical ECD calculation, and NMR computation using the GIAO method and DP4+ analysis. Among them, citreoviridins E‒H are four stereoisomers of a citreoviridin derivative, featuring a methylated α-pyrone, an oxidized polyene linker, and a tetrahydrofuran ring. Cytotoxicity assay of all isolates demonstrated that aureoterrolide N exhibited weak inhibitory effect against human cancer cell line HL-60 with an inhibition rate of 55.2% at 40.0 μM.

Biosynthesis of Epipyrone A Reveals a Highly Specific Membrane-Bound Fungal C-Glycosyltransferase for Pyrone Galactosylation

Epipyrone A is a unique C-galactosylated 4-hydroxy-2-pyrone derivative with an antifungal potential from the fungus Epicoccum nigrum. We elucidated its biosynthesis via heterologous expression and characterized an unprecedented membrane-bound pyrone C-glycosyltransferase biochemically. Molecular docking and mutagenesis experiments suggested a possible mechanism for the heterocyclic C-glycosylation and the importance of a transmembrane helix for its catalysis. These results expand the repertoire of C-glycosyltransferases and provide new insights into the formation of C-glycosides in fungi.

Enantiomeric α-pyrone derivatives with immunosuppressive activity from Talaromyces adpressus

Five pairs of undescribed enantiomeric α-pyrone derivatives (±)-adprepyrones A-E (±1-±5), together with an unreported congener adprepyrone F (6), and 6-[(E)-3-Hydroxyprop-1-enyl]-4-methoxy-5-methyl-2-pyrone (7), recently reported as synthetic compound, were isolated from the fungus Talaromyces adpressus. Their structures with absolute configurations were elucidated by HRESIMS, 1D and 2D NMR, electronic circular dichroism calculations, and single-crystal X-ray diffraction analyses. (±)-Adprepyrone A (±1) possesses an unreported carbon skeleton formed by the fusion of an α-pyrone derivative with nicotinamide. Compounds (+)-2, (±)-4, (±)-5, and 7 showed moderate inhibitory activity against concanavalin A (ConA)-induced T lymphocyte proliferation with IC50 values ranging from 8.9 to 19.8 μM.

Two pairs of 2-pyrone enantiomers and a benzophenone analogue from the endophytic fungus Penicillium egyptiacum

Four new 2-pyrone derivatives, two pairs of enantiomers, (±)-egypyrone A [(±)-1] and (±)-egypyrone B [(±)-2], together with a new benzophenone analogue, orbiophenone B (3), were isolated from the endophytic fungus Penicillium egyptiacum. The enantiomeric mixtures (±)-1 and (±)-2 were separated through chiral HPLC, respectively. Their structures were elucidated by extensive analysis of spectroscopic data and the absolute configuration was determined by comparing the optical rotation of structurally similar molecule. Subsequently, the cytotoxic activities of (±)-1, (±)-2, and 3 against the U87 cell line were tested and no activity was observed at a concentration of 10 µM.

Neuroprotective α-pyrones from Nigrospora oryzae, an endophytic fungus residing in Taxus chinensis var. mairei

Endophytes coevolve with plant hosts and thus are more probable to acquire the character (in favor) of producing undescribed bioactive metabolites. Consequently, the topic has been intensely investigated for over two decades, but endophytic metabolites with neuroprotective effect remain scarce. The study presents the discovery of eight undescribed (named solanapyrones U-Z and prosolanapyrones A and B) and six known pyrones (solanapyrones A-C and E-G) from the culture of Nigrospora oryzae, an endophytic fungus associated with Taxus chinensis var. mairei. The structures and absolute configurations of undescribed pyrones were elucidated by extensive spectroscopic analysis, modified Mosher's method, and induced circular dichroism (ICD) spectrum. Solanapyrones A and B and an undescribed pyrone (solanapyrone U) were demonstrated to be more neuroprotective than clenbuterol in inducing bone marrow mesenchymal stem cells (bMSCs) to secret nerve growth factor (NGF). The work updates the pyrone chemodiversity in nature and extends the biofunction repertoire of solanapyrone-related polyketides.

Unravelling the Secrets of α-Pyrones from Aspergillus Fungi: A Comprehensive Review of Their Natural Sources, Biosynthesis, and Biological Activities

Aspergillus, one of the most product-rich and genetically robust genera, contains a diverse range of species with potential economic and ecological implications. Chemically, Aspergillus is one of the essential sources of polyketides, alkaloids, diphenyl ethers, diketopiperazines, and other miscellaneous compounds, displaying a variety of pharmacological activities. The α-pyrones are unsaturated six-membered lactones. Although α-pyrone has a small structure, it is responsible for the structural diversity of several natural and synthetic compounds and multiple biological activities. In this review, we have summarized approximately 178 α-pyrone containing metabolites derivatives identified/reported from terrestrial, marine, endophytic, and filamentous Aspergillus species, including their sources, biological properties, and biosynthetic pathways until mid-2023, for the first time. This review is the first to compile and analyze the available data on α-pyrone metabolites from Aspergillus, which could facilitate further research and innovation in this field. Additionally, it offers a valuable source of scaffolds for future bioactive drug development, as some of these metabolites have shown potent antimicrobial, anti-inflammatory, and anticancer effects. Therefore, this review has significant implications for the advancement of natural product chemistry, pharmacology, biotechnology, and medicine.

Structurally Diverse Metabolites from the Marine-Derived Streptomyces sp. DS-27 Based on Two Different Culture Conditions

Nine new compounds, including streptothiomycin A-E (1-5), two cyclopentenones (6, 7), one α-pyrone (8), wailupemycin Q (20), along with sixteen known compounds were identified from a rhizosphere strain Streptomyces sp. DS-27 derived from the marine cordgrass Spartina alterniflora under two different culture conditions. All of the structures were elucidated by extensive analysis of 1D/2D NMR and HR-ESI-MS data. The absolute configurations were determined by NOESY analysis, ECD, specific rotation and GIAO NMR calculations, and DP4+ probability analysis. Bioactivity investigation showed that compounds 5 and 7 exhibited significant inhibitory effects on LPS-induced NO production in a dose-dependent manner, which indicates their anti-inflammatory potential.

Ethylidene-Tethered Chromene-Pyrone Hybrids as Potential Plant-Growth Regulators from an Endolichenic Phaeosphaeria Species

Phaeosphaeria sp., a lichen-associated fungus, produced six skeletally new dimeric spiciferones (1-6) and four known metabolites (7-10). The new structures were elucidated by spectroscopic analysis, and their absolute configurations were determined by electronic circular dichroism calculations. Compounds 1 and 3-6 represent the first examples of ethylidene-bridged dimers from the building blocks 4H-chromene-4,7(8H)-dione and α-pyrone, and 2 is a unique homodimer of spiciferone. Compounds 1, 2, and 5-9 significantly inhibited the growth of weed-like dicot Arabidopsis thaliana at 100.0 μM. Notably, 8 showed the strongest inhibitory activity against the fresh weight and root elongation of A. thaliana with the IC₅₀ values of 32.04 and 26.78 μM, respectively, whereas 1, 8, and 9 stimulated the growth of A. thaliana at lower concentrations. Meanwhile, compounds 2 and 6 exhibited weak inhibitory effects on the root elongation of monocot rice, while 1 and 8 exhibited growth-promoting effects on the shoot and root elongation of rice in a roughly dose-dependent manner.

Neuropyrones A-E, five undescribed α-pyrone derivatives with tyrosinase inhibitory activity from the endophytic fungus Neurospora dictyophora WZ-497

Five undescribed α-pyrone derivatives, named neuropyrones A-E, were isolated from the endophytic fungus Neurospora dictyophora WZ-497 derived from the stems of Aster tataricus L. f. The structures of these α-pyrones with absolute configurations were determined by comprehensive spectroscopic analysis and computational calculations. All isolated compounds were tested for various bioactivities, including tyrosinase inhibitory activity. The results showed that neuropyrones A-C displayed potent inhibitory effects on tyrosinase with IC₅₀ values of 0.38 ± 0.07, 0.49 ± 0.06, and 0.12 ± 0.01 mM, respectively, which were comparable to that of the positive control, kojic acid (IC₅₀ = 0.14 ± 0.021 mM). A molecular docking study revealed the interaction between 3 and the His263, His85, Val283, Asn260, Phe264, and Val248 residues of tyrosinase.

Inhibitory Effect of Styrylpyrone Extract of Phellinus linteus on Hepatic Steatosis in HepG2 Cells

The prevalence of nonalcoholic fatty liver disease (NAFLD) is estimated to be approximately about 25.24% of the population worldwide. NAFLD is a complex syndrome and is characterized by a simple benign hepatocyte steatosis to more severe steatohepatitis in the liver pathology. Phellinus linteus (PL) is traditionally used as a hepatoprotective supplement. Styrylpyrone-enriched extract (SPEE) obtained from the PL mycelia has been shown to have potential inhibition effects on high-fat- and high-fructose-diet-induced NAFLD. In the continuous study, we aimed to explore the inhibitory effects of SPEE on free fatty acid mixture O/P [oleic acid (OA): palmitic acid (PA); 2:1, molar ratio]-induced lipid accumulation in HepG2 cells. Results showed that SPEE presented the highest free radical scavenging ability on DPPH and ABTS, and reducing power on ferric ions, better than that of partitions obtained from n-hexane, n-butanol and distilled water. In free-fatty-acid-induced lipid accumulation in HepG2 cells, SPEE showed an inhibition effect on O/P-induced lipid accumulation of 27% at a dosage of 500 μg/mL. As compared to the O/P induction group, the antioxidant activities of superoxide dismutase, glutathione peroxidase and catalase were enhanced by 73%, 67% and 35%, respectively, in the SPEE group. In addition, the inflammatory factors (TNF-α, IL-6 and IL-1β) were significantly down-regulated by the SPEE treatment. The expressions of anti-adipogenic genes involved in hepatic lipid metabolism of 5' adenosine monophosphate (AMP)-activated protein kinase (AMPK), sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) were enhanced in the SPEE supplemented HepG2 cells. In the protein expression study, p-AMPK, SIRT1 and PGC1-α were significantly increased to 121, 72 and 62%, respectively, after the treatment of SPEE. Conclusively, the styrylpyrone-enriched extract SPEE can ameliorate lipid accumulation and decrease inflammation and oxidative stress through the activation of SIRT1/AMPK/PGC1-α pathways.

Experimental and Computational Studies on the Biotransformation of Pseudopyronines with Human Cytochrome P450 CYP4F2

The secondary metabolite pseudopyronine B, isolated from Pseudomonas mosselii P33, was biotransformed by human P450 enzymes, heterologously expressed in the fission yeast Schizosaccharomyces pombe. Small-scale studies confirmed that both CYP4F2 and CYP4F3A were capable of oxidizing the substrate, with the former achieving a higher yield. In larger-scale studies using CYP4F2, three new oxidation products were obtained, the structures of which were elucidated by UV-vis, 1D and 2D NMR, and HR-MS spectroscopy. These corresponded to hydroxylated, carboxylated, and ester derivatives (1-3) of pseudopyronine B, all of which had been oxidized exclusively at the ω-position of the C-6 alkyl chain. In silico homology modeling experiments highlighted key interactions between oxygen atoms of the pyrone ring and two serine residues and a histidine residue of CYP4F2, which hold the substrate in a suitable orientation for oxidation at the terminus of the C-6 alkyl chain. Additional modeling studies with all three pseudopyronines revealed that the seven-carbon alkyl chain of pseudopyronine B was the perfect length for oxidation, with the terminal carbon lying close to the heme iron. The antibacterial activity of the substrates and three oxidation products was also assessed, revealing that oxidation at the ω-position removes all antimicrobial activity. This study both increases the range of known substrates for human CYF4F2 and CYP4F3A enzymes and demonstrates their utility in producing additional natural product derivatives.

Computational Analysis of Triazole-Based Kojic Acid Analogs as Tyrosinase Inhibitors by Molecular Dynamics and Free Energy Calculations

Molecular docking, molecular dynamics (MD) simulations and the linear interaction energy (LIE) method were used here to predict binding modes and free energy for a set of 1,2,3-triazole-based KA analogs as potent inhibitors of Tyrosinase (TYR), a key metalloenzyme of the melanogenesis process. Initially, molecular docking calculations satisfactorily predicted the binding mode of evaluated KA analogs, where the KA part overlays the crystal conformation of the KA inhibitor into the catalytic site of TYR. The MD simulations were followed by the LIE method, which reproduced the experimental binding free energies for KA analogs with an r² equal to 0.97, suggesting the robustness of our theoretical model. Moreover, the van der Waals contributions performed by some residues such as Phe197, Pro201, Arg209, Met215 and Val218 are responsible for the binding recognition of 1,2,3-triazole-based KA analogs in TYR catalytic site. Finally, our calculations provide suitable validation of the combination of molecular docking, MD, and LIE approaches as a powerful tool in the structure-based drug design of new and potent TYR inhibitors.

In vivo characterization of key iridoid biosynthesis pathway genes in catnip (Nepeta cataria)

Using virus-induced gene silencing, we demonstrated that the enzymes GES, ISY, and MLPL are responsible for nepetalactone biosynthesis in Nepeta cataria. Nepetalactone is the main iridoid that is found in the Nepeta genus and is well-known for its psychoactive effect on house cats. Moreover, there is a burgeoning interest into the effect of nepetalactone on insects. Although the enzymes for nepetalactone biosynthesis have been biochemically assayed in vitro, validation of the role that these enzymes have in planta has not been demonstrated. Virus-induced gene silencing (VIGS) is a silencing method that relies on transient transformation and is an approach that has been particularly successful when applied to a variety of non-model plants. Here, we use a recently designed visual-marker dependent VIGS system to demonstrate that the nepetalactone biosynthetic enzymes GES, ISY, and MLPL impact nepetalactone biosynthesis in Nepeta cataria.

Chevalones H-M: Six New α-Pyrone Meroterpenoids from the Gorgonian Coral-Derived Fungus Aspergillus hiratsukae SCSIO 7S2001

Six new α-pyrone meroterpenoid chevalones H–M (1–6), together with six known compounds (7–12), were isolated from the gorgonian coral-derived fungus Aspergillus hiratsukae SCSIO 7S2001 collected from Mischief Reef in the South China Sea. Their structures, including absolute configurations, were elucidated on the basis of spectroscopic analysis and X-ray diffraction data. Compounds 1–5 and 7 showed different degrees of antibacterial activity with MIC values of 6.25–100 μg/mL. Compound 8 exhibited potent cytotoxicity against SF-268, MCF-7, and A549 cell lines with IC₅₀ values of 12.75, 9.29, and 20.11 μM, respectively.

Secondary Metabolites of Purpureocilliumlilacinum

Fungi can synthesize a wealth of secondary metabolites, which are widely used in the exploration of lead compounds of pharmaceutical or agricultural importance. Beauveria, Metarhizium, and Cordyceps are the most extensively studied fungi in which a large number of biologically active metabolites have been identified. However, relatively little attention has been paid to Purpureocillium lilacinum. P. lilacinum are soil-habituated fungi that are widely distributed in nature and are very important biocontrol fungi in agriculture, providing good biological control of plant parasitic nematodes and having a significant effect on Aphidoidea, Tetranychus cinnbarinus, and Aleyrodidae. At the same time, it produces secondary metabolites with various biological activities such as anticancer, antimicrobial, and insecticidal. This review attempts to provide a comprehensive overview of the secondary metabolites of P. lilacinum, with emphasis on the chemical diversity and biological activity of these secondary metabolites and the biosynthetic pathways, and gives new insight into the secondary metabolites of medical and entomogenous fungi, which is expected to provide a reference for the development of medicine and agrochemicals in the future.

Hybrids of 4-hydroxy derivatives of goniothalamin and piplartine bearing a diester or a 1,2,3-triazole linker as antiproliferative agents

A library of nine hybrids of 4-hydroxygoniothalamin (2), 4-hydroxypiplartine (4), monastrol (5) and oxo-monastrol (6) was prepared via a modular synthetic route with a diester or a 1,2,3-triazole as linkers. The compounds were assayed against a panel of human cancer cell lines, including MCF-7 (breast adenocarcinoma), HeLa (cervical adenocarcinoma), Caco-2 (colorectal adenocarcinoma) and PC3 (prostate adenocarcinoma), as well as against normal breast (MCF10A) and prostate (PNT2) cells. In general, hybrids with an ester linker containing 4-hydroxypiplartine (4) were more potent than the corresponding hybrids with 4-hydroxygoniothalamin (2). On the other hand, compounds presenting the 1,2,3-triazole linker displayed enhanced cytotoxicity and selectivity when compared to their corresponding hybrids with the diester linker. The 4-hydroxypiplartine-based hybrids 12 and 22 displayed high cytotoxicity (IC50 values below 10 μM) against all cancer cells studied, especially in MCF-7 cells with IC50 values of 1.7 ± 0.1 and 1.6 ± 0.9 μM, respectively. Furthermore, the 4-hydroxygoniothalamin-monastrol hybrid (compound 21) and the 4-hydroxypiplartine-oxo-monastrol hybrid (compound 25), both bearing a 1,2,3-triazole linker, displayed high selectivity and potency towards breast cancer cell line (MCF-7 vs. MCF10 cells, selectivity index = 15.8 and 7.1, respectively), while the 4-hydroxypiplartine -4-hydroxymethylgoniothalamin hybrid with a diester linker (compound 33) showed high selectivity towards melanoma cancer cells (selectivity index = 9.6). Antiproliferative and pro-apoptotic potential of compounds 12 and 22 against MCF-7 cancer cells were further investigated. Cell cycle studies revealed increased G2/M population in MCF-7 cultures as well as reduced G0/G1 population compared to the control groups indicating cell cycle arrest in G2/M phase. In addition, the frequency of positive cells for annexin V was higher in treated samples suggesting that compounds 12 and 22 induce apoptosis in estrogen-positive MCF-7 cells.

Comparative efficacy of resorbable fiber wraps loaded with gentamicin sulfate or gallium maltolate in the treatment of osteomyelitis

The high incidence of osteomyelitis associated with critical-sized bone defects raises clinical challenges in fracture healing. Clinical use of antibiotic-loaded bone cement as an adjunct therapy is limited by incompatibility with many antimicrobials, sub-optimal release kinetics, and requirement of surgical removal. Furthermore, overuse of antibiotics can lead to bacterial modifications that increase efflux, decrease binding, or cause inactivation of the antibiotics. Herein, we compared the efficacy of gallium maltolate, a new metal-based antimicrobial, to gentamicin sulfate released from electrospun poly(lactic-co-glycolic) acid (PLGA) wraps in the treatment of osteomyelitis. In vitro evaluation demonstrated sustained release of each antimicrobial up to 14 days. A Kirby Bauer assay indicated that the gentamicin sulfate-loaded wrap inhibited the growth of osteomyelitis-derived isolates, comparable to the gentamicin sulfate powder control. In contrast, the gallium maltolate-loaded wrap did not inhibit bacteria growth. Subsequent microdilution assays indicated a lower than expected sensitivity of the osteomyelitis strain to the gallium maltolate with release concentrations below the threshold for bactericidal activity. A comparison of the selectivity indices indicated that gentamicin sulfate was less toxic and more efficacious than gallium maltolate. A pilot study in a contaminated femoral defect model confirmed that the sustained release of gentamicin sulfate from the electrospun wrap resulted in bacteria density reduction on the surrounding bone, muscle, and hardware below the threshold that impedes healing. Overall, these findings demonstrate the efficacy of a resorbable, antimicrobial wrap that can be used as an adjunct or stand-alone therapy for controlled release of antimicrobials in the treatment of osteomyelitis.

Mechanisms and Dynamics of Synthetic and Biosynthetic Formation of Delitschiapyrones: Solvent Control of Ambimodal Periselectivity

The mechanism and dynamics for the formation of the delitschiapyrone family of natural products are studied by density functional theory (DFT) calculations and quasiclassical molecular dynamics simulations with DFT and xTB. In the uncatalyzed reaction, delitschiapyrones A and B are formed by Diels-Alder reactions through a single transition state and a post-transition state bifurcation that favors formation of delitschiapyrone B. In water and most likely in the enzyme, the acidic hydroxyquinone ionizes, and the resulting conjugate base undergoes cycloaddition preferentially to delitschiapyrone A. We demonstrate a new type of biosynthetic transformation and variable selectivity from a (4 + 2)/(4 + 3) ambimodal transition state.

Alternative Approach for Specific Tyrosinase Inhibitor Screening: Uncompetitive Inhibition of Tyrosinase by Moringa oleifera

Tyrosinase (TYR) is a type III copper oxidase present in fungi, plants and animals. The inhibitor of human TYR plays a vital role in pharmaceutical and cosmetic fields by preventing synthesis of melanin in the skin. To search for an effective TYR inhibitor from various plant extracts, a kinetic study of TYR inhibition was performed with mushroom TYR. Among Panax ginseng, Alpinia galanga, Vitis vinifera and Moringa oleifera, the extracts of V. vinifera seed, A. galanga rhizome and M. oleifera leaf reversibly inhibited TYR diphenolase activity with IC₅₀ values of 94.8 ± 0.2 µg/mL, 105.4 ± 0.2 µg/mL and 121.3 ± 0.4 µg/mL, respectively. Under the same conditions, the IC₅₀ values of the representative TYR inhibitors of ascorbic acid and kojic acid were found at 235.7 ± 1.0 and 192.3 ± 0.4 µg/mL, respectively. An inhibition kinetics study demonstrated mixed-type inhibition of TYR diphenolase by A. galanga and V. vinifera, whereas a rare uncompetitive inhibition pattern was found from M. oleifera with an inhibition constant of K_ii 73 µg/mL. Phytochemical investigation by HPLC-MS proposed luteolin as a specific TYR diphenolase ES complex inhibitor, which was confirmed by the inhibition kinetics of luteolin. The results clearly showed that studying TYR inhibition kinetics with plant extract mixtures can be utilized for the screening of specific TYR inhibitors.

Total Syntheses and Chemical Biology Studies of Hymeglusin and Fusarilactone A, Novel Circumventors of β-Lactam Drug Resistance in Methicillin-Resistant Staphylococcus aureus

Hymeglusin, a previously known eukaryotic hydroxymethylglutaryl-CoA (HMG-CoA) synthase inhibitor, was identified as circumventing the β-lactam drug resistance in methicillin-resistant Staphylococcus aureus (MRSA). We describe the concise total syntheses of a series of natural products, which enabled determination of the absolute configuration of fusarilactone A and provided structure-activity relationship information. Based on previous reports, we speculated that the target protein of this circumventing effect may be MRSA bacterial HMG-CoA synthase (mvaS). We found that this enzyme was dose-dependently inhibited by hymeglusin. Furthermore, overexpression of the MRSA mvaS gene and site-directed mutagenesis studies suggested its binding site and the mechanism of action.

In-vitro cytotoxicity in relation to chemotypic diversity in diploid and tetraploid populations of Gentiana kurroo Royle

ETHNOPHARMACOLOGICAL RELEVANCE

Gentiana kurroo is a multipurpose critically endangered medicinal herb prescribed as medicine in Ayurveda in India and exhibits various pharmacological properties including anti-cancer activity. The species is rich repository of pharmacologically active secondary metabolites together with secoiridoidal glycosides.

AIM OF THE STUDY

The study aimed to investigate the chemical diversity in different populations/cytotypes prevailing in G. kurroo to identify elite genetic stocks in terms of optimum accumulation/biosynthesis of desired metabolites and having higher in-vitro cytotoxicity potential in relation to chemotypic diversity.

MATERIAL AND METHODS

The wild plants of the species were collected from different ranges of altitudes from the Kashmir Himalayas. For cytological evaluation, the standard meiotic analysis was performed. The standard LC-MS/MS technique was employed for phytochemical analysis based on different marker compounds viz. sweroside, swertiamarin, and gentiopicroside. Different tissues such as root-stock, aerial parts, and flowers were used for chemo-profiling. Further, the methanolic extracts of diploid and tetraploid cytotypes were assessed for cytotoxic activity by using MTT assay against four different human cancer cell lines.

RESULTS

The quantification of major bioactive compounds based on tissue- and location-specific comparison, as well as in-vitro cytotoxic potential among extant cytotypes, was evaluated. The comprehensive cytomorphological studies of the populations from NW Himalayas revealed the occurrence of different chromosomal races viz. n = 13, 26. The tetraploid cytotype was hitherto unreported. The tissue-specific chemo-profiling revealed relative dominance of different phytoconstituents in root-stock. There was a noticeable increase in the quantity of the analyzed compounds in relation to increasing ploidy status along the increasing altitudes. The MTT assay of methanolic extracts of diploid and tetraploid cytotypes displayed significant cytotoxicity potential in tetraploids. The root-stock extracts of tetraploids were highly active extracts with IC₅₀ value ranges from 5.65 to 8.53 μg/mL against HCT-116 colon cancer.

CONCLUSION

The chemical evaluation of major bioactive compounds in diverse cytotypes from different plant parts along different altitudes presented an appreciable variability in sweroside, swertiamarin, and gentiopicroside contents. Additionally, the concentrations of these phytoconstituents varied for cytotoxicity potential among different screened cytotypes. This quantitative difference of active bio-constituents was in correspondence with the growth inhibition percentage of different tested cancer cell lines. Thus, the present investigation strongly alludes towards a prognostic approach for the identification of elite cytotypes/chemotypes with significant pharmacological potential.

Investigation of the Anti-Methicillin-Resistant Staphylococcus aureus Activity of (+)-Tanikolide- and (+)-Malyngolide-Based Analogues Prepared by Asymmetric Synthesis

Herein, we report antibacterial and antifungal evaluation of a series of previously prepared (+)-tanikolide analogues. One analogue, (4S,6S)-4-methyltanikolide, displayed promising anti-methicillin-resistant Staphylococcus aureus activity with a MIC of 12.5 µg/mL. Based on the antimicrobial properties of the structurally related (-)-malyngolide, two further analogues (4S,6S)-4-methylmalyngolide and (4R,6S)-4-methylmalyngolide bearing a shortened n-nonyl alkyl side chain were prepared in the present study using a ZrCl₄-catalysed deprotection/cyclisation as the key step in their asymmetric synthesis. When these were tested for activity against anti-methicillin-resistant Staphylococcus aureus, the MIC increased to 50 µg/mL.

Aromatic Polyketides and Hydroxamate Siderophores from a Marine-Algae-Derived Streptomyces Species

Four new aromatic polyketides, wailupemycins M-P (1-4), and two new hydroxamate siderophores, streptamides A (5) and B (6), together with the previously reported nocardamine (7), were isolated from the marine-algae-derived Streptomyces sp. OUCMDZ-3434. Wailupemycins M-P (1-4), possessing an α-pyrone moiety, were isolated from the extract of a liquid fermentation, and the siderophores (5-7) were isolated from the extract of a solid fermentation. Their structures were assigned based on detailed spectroscopic analysis and quantum chemical calculations. Compounds 5-7 were capable of binding Fe(III). Compound 5 can form a tighter Fe(III) complex than that of deferoxamine B mesylate (DFB).

New Era in the Treatment of Iron Deficiency Anaemia Using Trimaltol Iron and Other Lipophilic Iron Chelator Complexes: Historical Perspectives of Discovery and Future Applications

The trimaltol iron complex (International Non-proprietary Name: ferric maltol) was originally designed, synthesised, and screened in vitro and in vivo in 1980–1981 by Kontoghiorghes G.J. following his discovery of the novel alpha-ketohydroxyheteroaromatic (KHP) class of iron chelators (1978–1981), which were intended for clinical use, including the treatment of iron deficiency anaemia (IDA). Iron deficiency anaemia is a global health problem affecting about one-third of the world’s population. Many (and different) ferrous and ferric iron complex formulations are widely available and sold worldwide over the counter for the treatment of IDA. Almost all such complexes suffer from instability in the acidic environment of the stomach and competition from other dietary molecules or drugs. Natural and synthetic lipophilic KHP chelators, including maltol, have been shown in in vitro and in vivo studies to form stable iron complexes, to transfer iron across cell membranes, and to increase iron absorption in animals. Trimaltol iron, sold as Feraccru or Accrufer, was recently approved for clinical use in IDA patients in many countries, including the USA and in EU countries, and was shown to be effective and safe, with a better therapeutic index in comparison to other iron formulations. Similar properties of increased iron absorption were also shown by lipophilic iron complexes of 8-hydroxyquinoline, tropolone, 2-hydroxy-4-methoxypyridine-1-oxide, and related analogues. The interactions of the KHP iron complexes with natural chelators, drugs, metal ions, proteins, and other molecules appear to affect the pharmacological and metabolic effects of both iron and the KHP chelators. A new era in the treatment of IDA and other possible clinical applications, such as theranostic and anticancer formulations and metal radiotracers in diagnostic medicine, are envisaged from the introduction of maltol, KHP, and similar lipophilic chelators.

Penipyrols C-G and methyl-penipyrol A, α-pyrone polyketides from the mangrove derived fungus Penicillium sp. HDN-11-131

Six new α-pyrone polyketides, penipyrols C-G (1-5) and methyl-penipyrol A (6), together with one biogenetically related known compound, penipyrol A (7), were isolated from the extract of fungus Penicillium sp. HDN-11-131. Their structures including the absolute configurations were established by extensive spectroscopic analysis, Mosher's method, and ECD calculations as well as biogenic considerations. Compounds 1-4 possess a rare skeleton featuring γ-butyrolactone linked to α-pyrone ring through double bond. Compound 1 can induce pancreatic β-cell regeneration in zebrafish at 10 μM, which demonstrated promising anti-diabetes potential.

Analysis of Kojic Acid Derivatives as Competitive Inhibitors of Tyrosinase: A Molecular Modeling Approach

Tyrosinases belong to the functional copper-containing proteins family, and their structure contains two copper atoms, in the active site, which are coordinated by three histidine residues. The biosynthesis of melanin in melanocytes has two stages depending on the actions of the natural substrates L-DOPA and L-tyrosine. The dysregulation of tyrosinase is involved in skin cancer initiation. In the present study, using molecular modeling tools, we analyzed the inhibition activity of tyrosinase activity using kojic acid (KA) derivatives designed from aromatic aldehydes and malononitrile. All derivatives showed conformational affinity to the enzyme active site, and a favorable distance to chelate the copper ion, which is essential for enzyme function. Molecular dynamics simulations revealed that the derivatives formed promising complexes, presenting stable conformations with deviations between 0.2 and 0.35 Å. In addition, the investigated KA derivatives showed favorable binding free energies. The most stable KA derivatives showed the following binding free energies: -17.65 kcal mol-1 (D6), -18.07 kcal mol-1 (D2), -18.13 (D5) kcal mol-1, and -10.31 kcal mol-1 (D4). Our results suggest that these derivatives could be potent competitive inhibitors of the natural substrates of L-DOPA (-12.84 kcal mol-1) and L-tyrosine (-9.04 kcal mol-1) in melanogenesis.

pH-Dependent Photoinduced Interconversion of Furocoumaric and Furocoumarinic Acids

Photo-controlled or photo-regulated molecules, especially biologically active and operating in physiological conditions, are in steady demand. Herein, furocoumaric and furocoumarinic acids being (Z/E)-isomers relative to each other were obtained in two stages starting from psoralen: the alkaline solvolysis of psoralen led to furocoumaric acid, which was further Z → E photoisomerized (365 nm) to furocoumarinic acid. The kinetics of Z → E photoisomerization was monitored by HPLC and UV-vis spectrophotometry. Photophysical characteristics in the aqueous phase for both acids, as well as the reversibility of (Z/E) photoisomerization process, were also assessed. Furocoumarinic acid was found to be visibly fluorescent at pH 2.0-12.0, with the maxima of fluorescence emission spectra being pH-dependent. The reverse E → Z photoisomerization predicted by quantum chemistry calculations as energetically favorable for the monoanionic form of furocoumarinic acid was proved in the experiment while being complicated by pyrone ring closure back to psoralen in acidic and neutral conditions. The preparative synthesis of furocoumarinic acid outlined in this work is particularly valuable in view of a wide range of pharmacological effects previously predicted for this compound.

Machine Learning Prediction of Allosteric Drug Activity from Molecular Dynamics

Allosteric drugs have been attracting increasing interest over the past few years. In this context, it is common practice to use high-throughput screening for the discovery of non-natural allosteric drugs. While the discovery stage is supported by a growing amount of biological information and increasing computing power, major challenges still remain in selecting allosteric ligands and predicting their effect on the target protein's function. Indeed, allosteric compounds can act both as inhibitors and activators of biological responses. Computational approaches to the problem have focused on variations on the theme of molecular docking coupled to molecular dynamics with the aim of recovering information on the (long-range) modulation typical of allosteric proteins.

A Solvent-free, Catalyst-free Formal [3+3] Cycloaddition Dearomatization Strategy: Towards New Fluorophores for Biomolecules Labelling

A general, sustainable dearomatization reaction for nitrogen-containing heterocycles was developed. Under solvent free conditions and without catalyst, the biorenewable methyl coumalate (MC) reacted as an efficient C₃ partner to convert nine types of basic aromatic rings into their pyrido[1,2-a] fused derivatives in good to excellent yields. The fluorescence properties of some of the products were harnessed to conjugate fluorescent tags to bovine serum albumin (BSA) and immunoglobulin G.

Identification of Tyrosinase Inhibitors and Their Structure-Activity Relationships via Evolutionary Chemical Binding Similarity and Structure-Based Methods

Tyrosinase is an enzyme that plays a crucial role in the melanogenesis of humans and the browning of food products. Thus, tyrosinase inhibitors that are useful to the cosmetic and food industries are required. In this study, we have used evolutionary chemical binding similarity (ECBS) to screen a virtual chemical database for human tyrosinase, which resulted in seven potential tyrosinase inhibitors confirmed through the tyrosinase inhibition assay. The tyrosinase inhibition percentage for three of the new actives was over 90% compared to 61.9% of kojic acid. From the structural analysis through pharmacophore modeling and molecular docking with the human tyrosinase model, the pi–pi interaction of tyrosinase inhibitors with conserved His367 and the polar interactions with Asn364, Glu345, and Glu203 were found to be essential for tyrosinase–ligand interactions. The pharmacophore features and the docking models showed high consistency, revealing the possible essential binding interactions of inhibitors to human tyrosinase. We have also presented the activity cliff analysis that successfully revealed the chemical features related to substantial activity changes found in the new tyrosinase inhibitors. The newly identified inhibitors and their structure–activity relationships presented here will help to identify or design new human tyrosinase inhibitors.

Synthetic Routes to Coumarin(Benzopyrone)-Fused Five-Membered Aromatic Heterocycles Built on the α-Pyrone Moiety. Part 1: Five-Membered Aromatic Rings with One Heteroatom

This review gives an up-to-date overview of the different ways (routes) to the synthesis of coumarin (benzopyrone)-fused, five-membered aromatic heterocycles with one heteroatom, built on the pyrone moiety. Covering 1966 to 2020.

Modification of insulin amyloid aggregation by Zr phthalocyanines functionalized with dehydroacetic acid derivatives

Amyloid fibrils are widely studied both as target in conformational disorders and as basis for the development of protein-based functional materials. The three Zr phthalocyanines bearing dehydroacetic acid residue (PcZr(L1)2) and its condensed derivatives (PcZr(L2)2 and PcZr(L3)2) as out-of-plane ligands were synthesized and their influence on insulin fibril formation was studied by amyloid-sensitive fluorescent dye based assay, scanning electron microscopy, fluorescent and absorption spectroscopies. The presence of Zr phthalocyanines was shown to modify the fibril formation. The morphology of fibrils formed in the presence of the Zr phthalocyanines differs from that of free insulin and depends on the structure of out-of-plane ligands. It is shown that free insulin mostly forms fibril clusters with the length of about 0.3-2.1 μm. The presence of Zr phthalocyanines leads to the formation of individual 0.4-2.8 μm-long fibrils with a reduced tendency to lateral aggregation and cluster formation (PcZr(L1)2), shorter 0.2-1.5 μm-long fibrils with the tendency to lateral aggregation without clusters (PcZr(L2)2), and fibril-like 0.2-1.0 μm-long structures (PcZr(L3)2). The strongest influence on fibrils morphology made by PcZr(L3)2 could be explained by the additional stacking of phenyl moiety of the ligand with aromatic amino acids in protein. The evidences of binding of studied Zr phthalocyanines to mature fibrils were shown by absorption spectroscopy (for PcZr(L1)2 and PcZr(L2)2) and fluorescent spectroscopy (for PcZr(L3)2). These complexes could be potentially used as external tools allowing the development of functional materials on protein fibrils basis.

Asperginols A and B, Diterpene Pyrones, from an Aspergillus sp. and the Structure Revision of Previously Reported Analogues

Two new diterpene pyrones, asperginols A (1) and B (2), and four known analogues (3-6) were isolated from the endophytic fungus Aspergillus sp. HAB10R12. The structures and absolute configurations of these compounds were elucidated based on the analysis of their NMR, MS, and X-ray diffraction data. The revision of the absolute configurations at C-10, C-11, and C-14 of the known diterpene pyrones (3-6) and the determination of the configuration at the polyene side chain for compounds (4-6) were made using chemical methods and vibrational circular dichroism analysis. This group of diterpene pyrone compounds showed unique structural features including a 7/6/6 tricyclic diterpene moiety with an unusual trans-syn-trans stereochemical arrangement. Compound 6 showed moderate activity against the HT-29 colon cancer cell line.

Enantiomeric Dibenzo-α-Pyrone Derivatives from Alternaria alternata ZHJG5 and Their Potential as Agrochemicals

Three pairs of enantiomeric dibenzo-α-pyrone derivatives (1-3) including two pairs of new racemates (±)-alternaone A (1) and (±)-alternaone B (2) and one new enantiomer (-)-alternatiol (3), together with five known compounds (4-8) were isolated from the fungus Alternaria alternata ZHJG5. Their structures were confirmed by spectroscopic data and single-crystal X-ray diffraction analysis. All enantiomers were separated via chiral high-performance liquid chromatography, with their configurations determined by electronic circular dichroism calculation. Biogenetically, a key epoxy-rearrangement step was proposed for the formation of skeletons in 1-3; (+) 1, (-)-1, and 5 presented moderate antibacterial inhibition on phytopathogenic bacteria Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola. In the antifungal test, compounds 7 and 8 showed a moderate protective effect against Botrytis cinerea in vivo.

Synthesis of Pyranopyrans Related to Diplopyrone and Evaluation as Antibacterials and Herbicides

Stereoselective syntheses of new pyranopyrans that are related to the natural product diplopyrone, which is a phytotoxin implicated in cork oak decline, have been achieved from carbohydrate starting materials in two approaches that are based on C-glycosides as key intermediates. A C-alkynyl glycoside prepared by Ferrier rearrangement was used as the precursor to a new pyranopyran alkyne that showed potent antibacterial activity against the common bacterial pathogen Edwardsiella ictaluri that causes enteric septicemia in catfish. The C-alkynyl glycoside also showed herbicidal activity. New bioassay data for the pyranopyran nitrile (4aR,6S,8aR)-6-cyano-6,8a-dihydropyrano-[3,2-b]pyran-2(4aH)-one, the most potent of the pyranopyrans synthesized to date, were obtained in greenhouse studies that revealed additional herbicidal activity. Other new analogues that were synthesized included desmethylpyranopyrans that were prepared by Isobe C-alkynylation-rearrangement/reduction and RCM-based pyranopyran construction. The antibiotic and phytotoxic activities of the new pyranopyrans synthesized in this study highlight the importance of substituents on the nonlactone ring and demonstrate the potential of such compounds as antibiotics and herbicides.

Reckoning a fungal metabolite, Pyranonigrin A as a potential Main protease (Mpro) inhibitor of novel SARS-CoV-2 virus identified using docking and molecular dynamics simulation

The novel SARS-CoV-2 is the etiological agent causing the Coronavirus disease 2019 (COVID-19), which continues to become an inevitable pandemic outbreak. Over a short span of time, the structures of therapeutic target proteins for SARS-CoV-2 were identified based on the homology modelled structure of similar SARS-CoV transmission of 2003. Since the onset of the disease, the research community has been looking for a potential drug lead. Out of all the known resolved structures related to SARS-CoV, Main protease (Mpro) is considered an attractive anti-viral drug target on the grounds of its role in viral replication and probable non-interactive competency to bind to any viral host protein. To the best of our knowledge, till date only one compound has been identified and tested in-vivo as a potent inhibitor of Mpro protein, addressed as N3 (PubChem Compound CID: 6323191) and is known to bind irreversibly to Mpro suppressing its activity. Using computational approach, we intend to identify a probable natural fungal metabolite to interact and inhibit Mpro. After screening various small molecules for molecular docking and dynamics simulation, we propose Pyranonigrin A, a secondary fungal metabolite to possess potent inhibitory potential against the Main protease (Mpro) expressed in SARS-CoV-2 virus.

Synthesis of Deoxyradicinin, an Inhibitor of Xylella fastidiosa and Liberibacter crescens, a Culturable Surrogate for Candidatus Liberibacter asiaticus

Pierce's disease of grapevine and citrus huanglongbing are caused by the bacterial pathogens Xylella fastidiosa and Candidatus Liberibacter asiaticus (CLas), respectively. Both pathogens reside within the plant vascular system, occluding water and nutrient transport, leading to a decrease in productivity and fruit marketability and ultimately death of their hosts. Field observations of apparently healthy plants in disease-affected vineyards and groves led to the hypothesis that natural products from endophytes may inhibit these bacterial pathogens. Previously, we showed that the natural product radicinin from Cochliobolus sp. inhibits X. fastidiosa. Herein we describe a chemical synthesis of deoxyradicinin and establish it as an inhibitor of both X. fastidiosa and Liberibacter crescens, a culturable surrogate for CLas. The key to this three-step route is a zinc-mediated enolate C-acylation, which allows for direct introduction of the propenyl side chain without extraneous redox manipulations.

Binding and Release of FeIII Complexes from Glucan Particles for the Delivery of T1 MRI Contrast Agents

Yeast-derived β-glucan particles (GPs) are a class of microcarriers under development for the delivery of drugs and imaging agents to immune-system cells for theranostic approaches. However, the encapsulation of hydrophilic imaging agents in the porous GPs is challenging. Here, we show that the unique coordination chemistry of FeIII -based macrocyclic T1 MRI contrast agents permits facile encapsulation in GPs. Remarkably, GPs labeled with the simple FeIII complexes are stable under physiologically relevant conditions, despite the absence of amphiphilic groups. In contrast to the free FeIII coordination complex, the labeled FeIII -GPs have lowered T1 relaxivity and act as a silenced form of the contrast agent. Addition of a fluorescent tag to the FeIII complex produces a bimodal agent to further enable tracking of the nanoparticles and to monitor release. Treatment of the iron-labeled GPs with a maltol chelator or with mildly acidic conditions releases the intact iron complex and restores enhanced T1 relaxation of the water protons.

An Improved Nanoemulsion Formulation Containing Kojic Monooleate: Optimization, Characterization and In Vitro Studies

Tyrosinase inhibitors have become increasingly important targets for hyperpigmentation disease treatment. Kojic monooleate (KMO), synthesized from the esterification of kojic acid and oleic acid, has shown a better depigmenting effect than kojic acid. In this study, the process parameters include the speed of high shear, the time of high shear and the speed of the stirrer in the production of nanoemulsion containing KMO was optimized using Response Surface Methodology (RSM), as well as evaluated in terms of its physicochemical properties, safety and efficacy. The optimized condition for the formulation of KMO nanoemulsion was 8.04 min (time of high shear), 4905.42 rpm (speed of high shear), and 271.77 rpm (speed of stirrer), which resulted in a droplet size of 103.97 nm. An analysis of variance (ANOVA) showed that the fitness of the quadratic polynomial fit the experimental data with large F-values (148.79) and small p-values (p < 0.0001) and an insignificant lack of fit. The optimized nanoemulsion containing KMO with a pH value of 5.75, showed a high conductivity value (3.98 mS/cm), which indicated that the nanoemulsion containing KMO was identified as an oil-in-water type of nanoemulsion. The nanoemulsion remains stable (no phase separation) under a centrifugation test and displays accelerated stability during storage at 4, 25 and 45 °C over 90 days. The cytotoxicity assay showed that the optimized nanoemulsion was less toxic, with a 50% inhibition of cell viability (IC₅₀) > 500 μg/mL, and that it can inhibit 67.12% of tyrosinase activity. This study reveals that KMO is a promising candidate for the development of a safe cosmetic agent to prevent hyperpigmentation.

New chlamydosporol derivatives from the endophytic fungus Pleosporales sp. Sigrf05 and their cytotoxic and antimicrobial activities

Five new chlamydosporol derivatives, named pleospyrones A-E (1-5), together with one known congener (6), were isolated from the culture of the endophytic fungus Pleosporales sp. Sigrf05, obtained from the medicinal plant Siraitia grosvenorii. The structures of the new compounds were elucidated mainly by analysis of the HRESIMS, and (1D, 2D) NMR data, while ECD and optical rotation calculations were used to assign the absolute configurations. The plausible biosynthetic pathway of these compounds were proposed. The isolated compounds were evaluated for their cytotoxicity, antifungal and antibacterial activities. Compounds 1, and 4-6 were cytotoxic against the tested cancer cells with IC50 values of 1.26~47.5 μM. Compounds 1-3 showed moderate antifungal activities against Magnaporthe oryzae, while compound 5 displayed weak antibacterial activity.

Synthesis and characterization of maltol capped silver nanoparticles and their potential application as an antimicrobial agent and colorimetric sensor for cysteine

Maltol capped silver nanoparticles (McAgNPs) were synthesized using maltol (3-hydroxy-2-methyl-4-pyrone) as reducing and capping agent. McAgNPs were characterized by Visible and FTIR (Fourier transform infrared) spectroscopy, dynamic light scattering (DLS), and atomic force microscopy (AFM). Bright yellow color McAgNPs showed surface plasmon resonance (SPR) band at 436 nm, spherical shape and the average size between 35 to 50 nm. McAgNPs revealed higher stability against varying storage time, temperature, pH and salt concentrations. McAgNPs were successfully utilized for the selective and highly sensitive colorimetric detection of cysteine (Cys). Addition of Cys in a solution of McAgNPs, resulted a rapid change in color from yellow to orange because of the formation of nanoaggregates as confirmed by Visible/FTIR spectroscopy, DLS, and AFM studies. The estimated limit of detection (0.043 μM) was found to be more sensitive than previously reported other optical methods. The practical applicability of probe was also established by spiking the known concentrations of Cys in biological (blood plasma and urine) and environmental (tap and lake water) samples with significant recovery rates (92-104.6%). Despite being nontoxic to various tested cell lines, McAgNPs demonstrated potent antimicrobial, antibiofilm, and biofilm eradicating activities, thus potentially valuable in diagnostics and/or the synthesis of other nanocomposite material for broader applications.